1. Field of the Invention
The present invention relates to a method of forming a resin film in a desired pattern on a semiconductor substrate. It also relates to a semiconductor chip, a semiconductor package and a resist image remover.
2. Description of the Related Art
Heretofore, a specified polyimide resin has been employed as the resin of a resin film pattern. A semiconductor chip is produced in such a manner that; on a substrate, such as a silicon (Si) wafer, a gallium arsenide (GaAs) wafer, circuit elements are produced; the circuit elements are components, such as transistor, diode, resistance, capacitor, which constitute an electronic circuit; then, an inorganic insulator film made of any of SiO.sub.2 (silicon dioxide), Si.sub.3 N.sub.4 (Silicon nitride), PSG (phosphosilicate glass) etc., and metal wiring made of, for example aluminum, are formed so as to form a semiconductor substrate; further, for protecting a surface other than electrode parts to be external terminal for wiring, an insulator resin film is formed.
In this specification, the insulator resin film which protects a surface other than electrode parts on the semiconductor substrate calls a "resin film pattern".
It is known that the resin film pattern made of the specified polyimide resin is formed as stated below. Polyamic acid which is the precursor of the polyimide resin is dissolved in an organic solvent, and the semiconductor substrate of the silicon chip or the like is coated with the resulting solution. Thereafter, the substrate coated with the solution is processed by a method (a) wherein the substrate is heat-treated at 220-350 (.degree.C.), a resist image is subsequently formed on a resin film layer produced by the heat treatment, the resulting resin film is subsequently etched and removed with a hydrazine-based solution, and the resist image is finally removed from the resin film with a remover liquid of organic solvent type containing a phenolic compound (refer to, for example, the official gazette of Japanese Patent Application Laid-open No. 53401/1978), or by a method (b) wherein the substrate is heat-treated at 110-160 (.degree.C.), a resin film layer produced by the heat treatment is subsequently coated with a resist, the resist is subsequently exposed to light through a mask of a desired pattern (the non-exposed parts are to be a resist image), both the exposed parts of the resist and the underlying parts of the resin film are subsequently etched and removed with an alkaline aqueous solution, and the resulting resist image is finally removed from the resin film with a resist-image remover liquid which contains butyl acetate or any of cellosolves as a solvent (refer to, for example, the official gazette of Japanese Patent Application Laid-open No. 218008/1993).
The method (a) has the disadvantage that the harmful hydrazine-based solution (as an etchant) and the organic solvent containing the phenolic compound (as the resist-image remover liquid) are consumed in large quantities. On the other hand, the method (b) has the advantages of a simpler process etc. because the resist and the resin film can be simultaneously etched and removed. As compared with the method (a), accordingly, the method (b) is mainly applied at present.
The method (b), however, has the difficulty that the alkali employed as an etchant for resin film layer corrodes the aluminum wiring of the semiconductor substrate. It is therefore desired to develop a method which does not employ any alkali as the etchant, that is the method which employs organic solvent as the etchant.
Meanwhile, regarding the resin film pattern which is formed on the surface of the semiconductor substrate, it is demanded to lower the temperature for forming the resin film and to improve the characteristics of the resin film pattern, such as the heat resistance property, electric characteristics and hygroscopic property thereof. In view of these demands, it is also desired to develop a method in which polyimides or polyamides exhibiting superior solubilities in organic solvents, or engineering plastics such as polysulfone can be extensively used instead of the specified polyimide resin which is insoluble in organic solvents, having hitherto been employed.
Nevertheless, in the case where any of the resins of the superior solubilities in the organic solvent is used as the resin of the resin film pattern and where an organic solvent is used as the etchant, the resin used is dissolved in the organic solvent of either of the resist-image remover liquids employed in the methods (a) and (b), and hence, the resin film pattern cannot be formed.